1. Field of the Invention
This invention relates to a Cr-doped FeCoB based target material used for forming a soft magnetic thin-film, and a method for producing the target material.
2. Description of Related Art
The recent progress in the magnetic recording technology is remarkable, and the record densities of magnetic record media are being heightened for increasing capacities of drives. In the magnetic record media for the longitudinal magnetic recording systems currently used worldwide, however, an attempt to realize a high record density leads to refined record bits, which require a high coercivity to such an extent that recording cannot be made with the record bits. In view of this, a perpendicular magnetic recording system is under study as a means of solving these problems and improving the record densities.
The perpendicular magnetic recording system is a system in which a magnetization-easy axis is oriented in the direction vertical to a medium surface in the magnetic film of the perpendicular magnetic record medium, and is suitable for high record densities. In addition, as for the perpendicular magnetic recording system, a two-layered record medium has been developed having a magnetic record film layer where the record sensitivity is improved and a soft magnetic film layer. A CoCrPt—SiO2 based alloy is generally used in the magnetic record film layer.
On the other hand, examples of known soft magnetic layers are as follows. Japanese Patent Laid-Open Publication No. 346423/2004 discloses a Fe—Co—B based alloy target material in which the diameter of the maximum inscribed circle which can be drawn in a region with no boride phase in a cross-microstructure is equal to 30 μm or less. Japanese Patent Laid-Open Publication No. 320627/2005 discloses a method for producing a Co alloy target material comprising 1 to 10 atom % Zr and 1 to 10 atom % Nb and/or Ta, and the balance being essentially Co, suggesting that quenching treatment is performed on a molten Co alloy to produce alloy powder, and then the alloy powder having a particle size of 500 μm or less is pressed and sintered to obtain a Co alloy target material.
Magnetron sputtering method is generally used for the preparation of the aforementioned soft magnetic film. This magnetron sputtering method is a method in which a magnet is disposed behind a target material to leak the magnetic flux onto a surface of the target material for converging plasma in the leaked magnetic flux region, enabling a high-speed coating. Since the magnetron sputtering method has a feature of leaking the magnetic flux on the sputtering surface of the target material, in the case where magnetic permeability of the target material itself is high, it is difficult to form, on the sputtering surface of the target material, the leaked magnetic flux necessary and sufficient for the magnetron sputtering method. In view of this, Japanese Patent Laid-Open Publication No. 346423/2004 is proposed for a demand for reducing the magnetic permeability of the target material itself as much as possible.
However, the maximum thickness of the target product produced as described above is approximately 5 mm. If the thickness exceeds 5 mm, leaked magnetic flux is insufficiently created on the surface of the target material, resulting in the impossibility of normal magnetron sputtering. A Fe-based material is desired since a high magnetic flux density is required for a film of a target material used for the magnetron sputtering. In this case, however, corrosion resistance is unsatisfied, while there are problems that the oxidation of the target material degrades the film quality and that an abnormal discharge occurs in an oxidized area during the sputtering process to result in sputtering failure.